In recent years, it has become necessary to miniaturize electronic parts and reduce the thickness thereof without inviting deterioration in the performance and quality over conventional electronic parts in accordance with the miniaturization of electronic equipment such as portable information terminals and portable communication devices. This also applies to piezoelectric parts such as a piezoelectric resonator, a piezoelectric transformer, a piezoelectric gyro, a piezoelectric buzzer and a piezoelectric actuator. In particular, with respect to energy confining type resonance utilizing piezoelectric resonators, a thin surface-mountable resonator has been developed. In this case, the support and fixing of the resonator has been carried out by directly mounting a piezoelectric substrate provided with an exciting electrode on an electrode formed on a base plate, without the use of any support, and effecting a bonding by means of a conductive cement.
With respect to resonance vibration utilizing parts other than the piezoelectric resonator, such as a piezoelectric transformer, a piezoelectric gyro, a piezoelectric buzzer or a piezoelectric actuator, the following method for supporting and fixing of the piezoelectric substrate thereof is proposed. Namely, the support and fixing of the piezoelectric substrate thereof is carried out by arranging a stringy rubber-made elastic body or the like on a line (surface) along nodal points of resonance vibration occurring in the direction of vibration of the piezoelectric substrate so as not to inhibit resonance vibration. In addition, a lead terminal is soldered on an exciting electrode provided on the piezoelectric substrate so that removing the electrode can be attained (see Japanese Patent Laid-open Publication No. 8(1996)-32135). The "exciting electrode" refers to the electrode to vibrate the piezoelectric vibrating element by exerting alternating current voltages to the piezoelectric vibrating elements. Furthermore, another method has been proposed in which a lead terminal is a metal spring is elastically bonded to the piezoelectric substrate so that the support and fixing thereof and the electrode taking-off are simultaneously carried out (see Japanese Patent Laid-open Publication No. 8(1996)-298213). Further, a structure has been proposed in which a spring piece is interposed between a piezoelectric substrate accommodating a cage-shaped outer trim case and a piezoelectric substrate. The spring piece protrudes from the outer trim case so as to use it as an input terminal (see Japanese Patent Laid-open Publication No. 7(1995)-079029).
Generally, the above piezoelectric parts are often assembled in portable devices which are used in dynamic conditions, so that it is demanded that the impact resistance and frequency temperature characteristic thereof be maintained well.
However, in the above supporting fixing method comprising bonding a piezoelectric substrate onto a base plate by means of a conductive cement, the temperature dependent expansion coefficient is different between the piezoelectric substrate and the base plate. As a result, upon the occurrence of a temperature change, the piezoelectric substrate comes to have a stress, thereby inviting the danger that the frequency characteristic is changed. Further, in this method, the bonding is conducted without the use of a cushioning material, so that, when a strong bonding to the base plate is conducted for improving the impact resistance, the frequency temperature characteristic thereof is unfavorably deteriorated.
On the other hand, in the above method of effecting the supporting and fixing by means of a rubber-made elastic body, a metal spring or a spring piece, such a supporting position, supporting method, driving method and electrode takeoff method as will not inhibit the vibration of the piezoelectric substrate are required. Therefore, this causes a problem of securing the performance of piezoelectric parts such as a piezoelectric actuator, a piezoelectric gyro, a piezoelectric transformer or a piezoelectric buzzer which is used in a large-amplitude resonance vibration of the piezoelectric substrate.
Moreover, in the supporting and fixing in which the rubbery elastic body is used, for attaining an electrical connection with the piezoelectric substrate, it is required to separately solder a lead terminal onto an exciting electrode to thereby take off an electrode. Further, in this method, even when the support by means of the stringy elastic body is performed on the line along the nodal points of resonance vibration occurring in the direction of excitation of the piezoelectric substrate, the displacement of piezoelectric substrate in the directions other than the excitation direction which occurs by the resonance vibration is inhibited to thereby inhibit the resonance vibration. Other methods are also applicable which include one employing a wire or another comprising elastically bonding a pin. In all of these methods, the number of parts is increased and the assembly work is complicated to thereby bring about problems of productivity and cost.
Therefore, for securely supporting the piezoelectric substrate by means of the elastic body, it is contemplated to expand the width of the elastic body and the area of contact thereof with the piezoelectric substrate. However, this leads to an increase of the area of the upper surface of piezoelectric substrate covered by the elastic body, so that, unfavorably, not only the mechanical vibration of the piezoelectric substrate is inhibited but also the miniaturization of the piezoelectric part becomes difficult.
Furthermore, in the method in which the piezoelectric substrate is fixed in a piezoelectric substrate accommodating cage-shaped outer trim case by means of a spring piece, there is the fear that the positions of the spring piece and the piezoelectric substrate are dislocated from each other by, for example, vibration impact. When the piezoelectric substrate is brought into contact with the outer trim case, the vibration of the piezoelectric substrate is unfavorably inhibited to an extreme degree.
In Japanese Patent Laid-open Publication No. 55(1980)-100719, a piezoelectric substrate supporting structure is proposed in which a piezoelectric substrate electrode and an electrode coating on a circuit substrate are supported by rubber contact points composed of a conductive rubber to thereby effect communication therebetween. However, in this structure, the rubber contact points per se must be fixed by disposing recesses for burying the rubber contact points in the electrode coating on the circuit substrate or by separately forming a silicon rubber coating on the top of the electrode coating, so that the structure is unfavorably complicated. Further, in this structure, the above rubber contact points prevent realizing a large elastic displacement, to possibly inhibiting the vibration of the piezoelectric substrate. Still further, there is the fear of deterioration of rubber contact points by contact with, for-example, air to thereby unfavorably result in inhibition of the functions of the piezoelectric substrate. In all the above proposals, the vibration produced by the driving of the piezoelectric substrate is propagated to the base plate and the outer trim case to thereby unfavorably cause generation and expansion of audible components of vibration leading to sounding (noisemaking).